The brown sugar taste/flavor is lost during the heat of fermentation. Some have added it after 5 days. I have not tried that. There may be a steep grain that will impart the molasses taste you are expecting from brown sugar.
Others have used a slight addition of molasses but I read you have to be carefull. I added 1 oz to a 2.5g recipe of Jamaican Mon, it was good
*Simcoe hops are best for IPA PA. Fuggles is great for darks mostly used for aroma and flavor
Perle is for German Ale Wheat Pils.
Might consider Northern?
Of course its your beer
Sometimes good to go for it
* I use this link to learn about hops, best resource I have found. I spend 'hours' reading this
I had a dark Oatmeal Stout all extract get stuck at FG 1.022. I bottles anyway, turned out great.
I do like dark porter and stouts. Might suggest as 'steve' said and change out the amber LME for a light LME and try another dark steep grain.
*I am not an expert on steeping just moving to that method.